Art-studio subject (4)
I believe the answer is:
nude
I believe this clue is a double definition.
'art' is the first definition.
(nude is a kind of art)
'studio subject' is the second definition.
(I've seen this in another clue)
(Other definitions for nude that I've seen before include "Flesh-coloured" , "Having nothing on" , "Completely unclothed" , "totally exposed" , "Naked art subject" .)